1. Field of the Invention
This invention relates to a thermoplastic resin sheet having electrical conductivity on the surface thereof.
2. Description of the Related Art
Processes for making thermoplastics electroconductive include a process of blending an antistatic agent with thermoplastics or applying the agent on the surface of the thermoplastic molded product and a process of blending carbon black as an electroconductive material with thermoplastics. However, in the case of the former process, the surface resistivity of the resulting product is at most about 10.sup.9 .OMEGA./.quadrature. and yet there are drawbacks that the surface resistivity changes due to the ambient humidity; the antistatic effect is lost with lapse of time; etc. Further, in the case of the latter process, unless the more continuously the carbon black particles are present inside the thermoplastic resin sheet, the more the quantity thereof blended is increased, the aimed electrical conductivity cannot be obtained. However, if a large quantity of carbon black is blended, there are drawbacks that the mechanical strength of the molded product is notably reduced and the processability of the thermoplastic resin becomes inferior.
As electroconductive thermoplastic resin sheets solving the above-mentioned so far raised problems, an electroconductive thermoplastic resin sheet having a non-woven fabric consisting of electroconductive fibers and hot-melt-adhesive fibers (hereinafter referred to as electroconductive non-woven fabric) melt-adhered onto a thermoplastic resin sheet as a substrate is disclosed in Japanese patent application laid-open No. Sho 58-155917/1983, and an electroconductive thermoplastic resin sheet having a knitted or woven fabric consisting of electroconductive fibers and hot-melt-adhesive fibers melt-adhered onto and integrated with a thermoplastic resin sheet as a substrate is disclosed in Japanese patent application laid-open No. Sho 58-166035/1983.
However, electroconductive thermoplastic resin sheets obtained according to these processes have drawbacks that merely by slightly abrading the surface of the sheets by nails, clothes, etc., a portion of the electroconductive fibers present on the surface layer thereof peels off from the substrates to cause fluffing. Such a fluffing phenomenon not only makes the appearance of the electroconductive thermoplastic resin sheet inferior, but also when the sheets are strongly abraded, electroconductive fibers peel off from the sheets to contaminate the environment and further deteriorate the electroconductive performance; hence these facts have been becoming a serious obstacle to practical use of such sheets.